A Rapid High-Performance Liquid Chromatography Method to Measure Linezolid and Daptomycin Concentrations in Human Plasma

Impact on Antibiotic Resistance, Therapeutic Success, and Control of Side Effects in Therapeutic Drug Monitoring (TDM) of Daptomycin: A Scoping Review

Antimicrobial resistance (AR) is a problem that threatens the search for adequate safe and effective antibiotic therapy against multi-resistant bacteria like methicillin-resistant Staphylococcus aureus (MRSA), and vancomycin-resistant Enterococci (VRE) and Clostridium difficile, among others. Daptomycin is the treatment of choice for some infections caused by Gram-positive bacteria, indicated most of the time in patients with special clinical conditions where its high pharmacokinetic variability (PK) does not allow adequate plasma concentrations to be reached. The objective of this review is to describe the data available about the type of therapeutic drug monitoring (TDM) method used and described so far in hospitalized patients with daptomycin and to describe its impact on therapeutic success, suppression of bacterial resistance, and control of side effects. The need to create worldwide strategies for the appropriate use of antibiotics is clear, and one of these is the performance of therapeutic drug monitoring (TDM). TDM helps to achieve a dose adjustment and obtain a favorable clinical outcome for patients by measuring plasma concentrations of an administered drug, making a rational interpretation guided by a predefined concentration range, and, thus, adjusting dosages individually.

Observational study to determine the optimal dose of daptomycin based on pharmacokinetic/pharmacodynamic analysis

High doses of daptomycin (DAP) (>6 mg/kg/day) have been preliminarily recommended in recent practical guidelines for methicillin-resistant Staphylococcus aureus infection, to achieve better clinical effects. While such doses can elevate the plasma trough concentration (Cmin) of DAP, there is an associated risk of creatine phosphokinase (CPK) elevation warranting further investigation. In the current study relationships between DAP Cmin and CPK elevation were investigated, and optimal DAP doses were determined. Plasma DAP concentrations were measured in 20 patients. Logistic regression analysis was performed to assess relationships between DAP Cmin and CPK elevation, then a population pharmacokinetic model of DAP was developed. To determine an optimal DAP dose a Monte Carlo simulation (MCS) was performed to minimize the risk of CPK elevation and maximize the probability of successful treatment. In logistic regression analysis DAP Cmin was significantly associated with CPK elevation (odds ratio 1.21, p = 0.048). With respect to dose-dependent increases in the probability of CPK elevation and exposure to DAP, MCS estimated an optimal DAP dose of 4-6 mg/kg/day, corresponding to a minimum inhibitory concentration (MIC) of ≤0.5 μg/mL. For an MIC of 1 μg/mL, MCS estimated an optimal DAP dose of 10 mg/kg/day. However, the probability of CPK elevation associated with high doses of DAP was higher than that associated with the approved doses. In cases where high doses of DAP are administered, close CPK monitoring is required and therapeutic drug monitoring of DAP may be desirable.

Daptomycin Dose-Ranging Evaluation with Single-Dose versus Multidose Ceftriaxone Combinations against Streptococcus mitis/oralis in an Ex Vivo Simulated Endocarditis Vegetation Model

The viridans group streptococci (VGS) are a heterogeneous group of organisms which are important components of the normal human oral flora. Among the VGS, the Streptococcus mitis /oralis subgroup is one of the most common causes of infective endocarditis (IE). Daptomycin (DAP) is a potential alternative therapeutic option for invasive S. mitis infections, given high rates of β-lactam resistance and vancomycin tolerance in such strains. However, the ability of these strains to rapidly evolve high-level and durable DAP resistance (DAP-R) is problematic. Recent data suggest that combination DAP-β-lactam therapy circumvents this issue. Human-simulated dose-escalating DAP-alone dose regimens (6, 8, 10, or 12 mg/kg/day times 4 days) versus DAP (6 mg/kg/day) plus ceftriaxone (CRO) (2 g once daily times 4 days or 0.5 g, single dose) were assessed against two prototypical DAP-susceptible (DAP-S) S. mitis /oralis strains (SF100 and 351), as measured by a pharmacokinetic/pharmacodynamic (PK/PD) model of simulated endocardial vegetations (SEVs). No DAP-alone regimen was effective, with regrowth of high-level DAP-R isolates observed for both strains over 96-h exposures. Combinations of DAP-CRO with either single- or multidose regimens yielded significant reductions in log₁₀ CFU/g amounts within SEVs for both strains (∼6 log₁₀ CFU/g) within 24 h. In addition, no DAP-R strains were detected in either DAP-CRO combination regimens over the 96-h exposure. In contrast to prior in vitro studies, no perturbations in two key cardiolipin biosynthetic genes (cdsA and pgsA) were identified in DAP-R SEV isolates emerging from strain 351, despite defective phospholipid production. The combination of DAP-CRO warrants further investigation for treatment of IE due to S. mitis /oralis.

A critical review of HPLC-based analytical methods for quantification of Linezolid

Linezolid is a synthetic antimicrobial agent belonging to the oxazolidinone class. Since its approval in the year 2000 until now, linezolid remains the main representative drug for the oxazolidinone class of drugs, which is used in therapy due to its unique mode of action, which involves inhibition of protein synthesis. As linezolid holds great importance in antimicrobial therapy, it is necessary to compile the various analytical methods that have been reported in the literature for its analysis. Analytical techniques used for pharmaceutical analyses and therapeutic drug monitoring play an important role in comprehending the aspects regarding bioavailability, bioequivalence, and therapeutic monitoring during patient follow-ups. Even though linezolid has had the approval for clinical use for more than 18 years now, most of the analytical methods for its determination reported in the scientific literature are the ones which utilize HPLC. Therefore, the present review provides a summary of the HPLC-based methods used in the determination and quantification of linezolid in different matrices since the time of its discovery.

Linezolid-A Review of Analytical Methods in Pharmaceuticals and Biological Matrices

Bacterial resistance to antibiotics is a growing phenomenon in the world. Considering the relevance of antimicrobials for population and the reduction in the registration of new antimicrobials by regulatory agencies, proper quality control is required to minimize the spread of bacterial resistance and ensure the effectiveness of a treatment, as well as safety for the patient. The recent addition to the antimicrobial world is the oxazolidinone classes of antibiotics, especially useful to treat infections caused by Gram-positive bacteria. Eperezolid and linezolid (LIN) are the two members of the oxazolidinone class of antibiotics. LIN was the first oxazolidinone approved by the Food and Drug Administration. The present review focuses on the analytical methods for the assessment of LIN in pharmaceuticals and biological matrices. The critical validation parameters like the linearity, limit of detection, limit of quantification are discussed for the individual method. Also the critical quality attributes like the sensitivity and the sample preparation techniques for bioanalytical methods are also discussed. Furthermore, some future trends that can be incorporated in the determination of similar drugs are also suggested.

Influence of Inoculum Effect on the Efficacy of Daptomycin Monotherapy and in Combination with β-Lactams against Daptomycin-Susceptible Enterococcus faecium Harboring LiaSR Substitutions

Enterococcus faecium isolates that harbor LiaFSR substitutions but are phenotypically susceptible to daptomycin (DAP) by current breakpoints are problematic, since predisposition to resistance may lead to therapeutic failure. Using a simulated endocardial vegetation (SEV) pharmacokinetic/pharmacodynamic (PK/PD) model, we investigated DAP regimens (6, 8, and 10 mg/kg of body weight/day) as monotherapy and in combination with ampicillin (AMP), ceftaroline (CPT), or ertapenem (ERT) against E. faecium HOU503, a DAP-susceptible strain that harbors common LiaS and LiaR substitutions found in clinical isolates (T120S and W73C, respectively). Of interest, the efficacy of DAP monotherapy, at any dose regimen, was dependent on the size of the inoculum. At an inoculum of ∼10⁹ CFU/g, DAP doses of 6 to 8 mg/kg/day were not effective and led to significant regrowth with emergence of resistant derivatives. In contrast, at an inoculum of ∼10⁷ CFU/g, marked reductions in bacterial counts were observed with DAP at 6 mg/kg/day, with no resistance. The inoculum effect was confirmed in a rat model using humanized DAP exposures. Combinations of DAP with AMP, CPT, or ERT demonstrated enhanced eradication and reduced potential for resistance, allowing de-escalation of the DAP dose. Persistence of the LiaRS substitutions was identified in DAP-resistant isolates recovered from the SEV model and in DAP-resistant derivatives of an initially DAP-susceptible clinical isolate of E. faecium (HOU668) harboring LiaSR substitutions that was recovered from a patient with a recurrent bloodstream infection. Our results provide novel data for the use of DAP monotherapy and combinations for recalcitrant E. faecium infections and pave the way for testing these approaches in humans.

Daptomycin Pharmacokinetics and Pharmacodynamics in Septic and Critically Ill Patients

Infections, including sepsis, are associated with high mortality rates in critically ill patients in the intensive care unit (ICU). Appropriate antibiotic selection and adequate dosing are important for improving patient outcomes. Daptomycin is bactericidal in bloodstream infections caused by Staphylococcus aureus and other Gram-positive pathogens cultured in ICU patients. The drug has concentration-dependent activity, and the area under the curve/minimum inhibitory concentration ratio is the pharmacokinetic/pharmacodynamic (PK/PD) index that best correlates with daptomycin activity, whereas toxicity correlates well with daptomycin plasma trough concentrations (or minimum concentration [C min]). Adequate daptomycin exposure can be difficult to achieve in ICU patients; multiple PK alterations can result in highly variable plasma concentrations, which are difficult to predict. For this reason, therapeutic drug monitoring could help clinicians optimize daptomycin dosing, thus improving efficacy while decreasing the likelihood of serious adverse events. This paper reviews the literature on daptomycin in ICU patients with sepsis, focusing on dosing and PK and PD parameters.

Daptomycin: Physicochemical, Analytical, and Pharmacological Properties

Daptomycin is the first approved member of a new class of antimicrobials, the cyclic lipopeptides, and presents selective action against gram-positive bacteria, including methicillin- and vancomycin-resistant strains. Considering that resistance to daptomycin is rare, the drug has become very important for current clinical practice. This review covers daptomycin's physicochemical characteristics, antibacterial spectrum, mechanism of action, pharmacokinetics, clinical applications, side effects, drug interactions, and the analytical methods used to measure daptomycin in pharmaceutical products and biologic samples. Special attention has been given to therapeutic drug monitoring reports, as studies have shown its highly variable pharmacokinetics in specific circumstances, such as in patients suffering from critical illness, morbid obesity, severe sepsis, and kidney injury. For the same reason, methods described for therapeutic drug monitoring of daptomycin in the special patient population have been reviewed. In addition, the review presents a discussion of environmentally friendly analytical methods for daptomycin, which are necessary to reduce the impact of our activities on the environment. However, it was observed that there is a gap in the literature in this regard and further research involving the development of "green" methodologies for the analysis of daptomycin is necessary. The review will be useful to the clinical community in assisting with the responsible use of daptomycin, which is critical to prevent the emergence of resistant strains.

A green approach for the quantification of daptomycin in pharmaceutical formulation by UV spectrophotometry

abstract Daptomycin is the first approved drug from a new class of antimicrobials, the cyclic lipopeptides, and is a very important antimicrobial agent in current clinical practice. Currently, there are no "green" analytical methods described in the literature to analyze the typical pharmaceutical dosage form of daptomycin. Thus, the aim of this work was to validate an environment-friendly spectrophotometric method in the UV region, for the analysis of daptomycin as a lyophilized powder. Water was used as diluent and the analyses were carried out on a spectrophotometer at 221 nm. The method met all validation requirements of the ICH guidelines, over a concentration range of 6-21 µg mL-1. A Student's t-test demonstrated that the proposed method was comparable to an HPLC method previously validated. Thus, the validated spectrophotometric method could quantify daptomycin in a powder form for injectable solutions, while being an economical, rapid, and "green" alternative for routine analysis in quality control.

In Vitro Activities of Novel Antimicrobial Combinations against Extensively Drug-Resistant Acinetobacter baumannii

Extensively drug-resistant (XDR) Acinetobacter spp. have emerged as a cause of nosocomial infections, especially under conditions of intensive care. Unfortunately, resistance to colistin is increasing and there is a need for new therapeutic options. We aimed to study the effect of some novel combinations against XDR Acinetobacter baumannii in an in vitro pharmacokinetics-pharmacodynamics (PK/PD) model. Three nonrelated clinical strains of XDR A. baumannii were investigated. Antibiotic-simulated regimens were colistin at 3 MU every 8 h (q8h) (first dose, 6 MU), daptomycin at 10 mg/kg of body weight q24h, imipenem at 1 g q8h, and ertapenem at 1 g q24h. Combination regimens included colistin plus daptomycin, colistin plus imipenem, and imipenem plus ertapenem. Samples were obtained at 0, 1, 2, 4, 8, and 24 h. Among the single-agent regimens, only the colistin regimen resulted in significant reductions in log10 CFU per milliliter compared to the control for all the strains tested. Although colistin achieved bactericidal activity at 4 h, it was not able to reach the limit of detection (1 log10 CFU/ml). One strain had significant regrowth at 24 h without the emergence of resistance. Daptomycin-colistin combinations led to a significant reduction in levels of log10 CFU per milliliter that were better than those achieved with colistin as a single-agent regimen, reaching the limit of detection at 24 h against all the strains. The combination of imipenem plus ertapenem outperformed the colistin regimen, although the results did not reach the limit of detection, with significant regrowth at 24 h. Similarly, colistin-plus-imipenem combinations reduced the levels of log10 CFU per milliliter at 8 h, with significant regrowth at 24 h but with development of resistance to colistin. We have shown some potentially useful alternatives for the treatment of extensively drug-resistant A. baumannii. Among them, the daptomycin-colistin combination was the most effective and should be investigated in future studies.

Rapid Turbidimetric Assay to Determine the Potency of Daptomycin in Lyophilized Powder

Daptomycin is an important antimicrobial for clinical practice, mainly because it remains very active against Gram-positive resistant strains, such as methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci. Development of microbiological methods for the analysis of antimicrobials is highly recommended, since they can provide important information about their biological activities, which physicochemical methods are not able to provide. Considering that there are no studies in the literature describing microbiological methods for the analysis of daptomycin, the aim of this work was to validate a microbiological method for the quantitation of daptomycin by the turbidimetric assay. Staphylococcus aureus was used as the test microorganism, and the brain heart infusion broth was used as the culture medium. The validation of the method was performed according to the ICH guidelines, and it was shown to be linear, precise, robust, accurate and selective, over a concentration range of 8.0 to 18.0 µg mL-1. Student's t-test showed the interchangeability of the proposed method with a previously-validated HPLC method. The developed turbidimetric method described in this paper is a convenient alternative for the routine quality control of daptomycin in its pharmaceutical dosage form.

Pharmacokinetics and skin-tissue penetration of daptomycin in rats

Background

Daptomycin is recommended for complicated skin and skin-structure infections. However, information on the penetration of daptomycin into skin is limited. Therefore, the aim of this in vivo investigation was to determine the pharmacokinetics and skin penetration of daptomycin in rats.

Materials and methods

Concentrations of daptomycin were determined by high-performance liquid chromatography. A noncompartmental pharmacokinetic analysis was conducted to estimate the rate and extent of daptomycin penetration from the systemic circulation into skin tissue. Since protein binding of daptomycin in rat serum was 89.3%, the free maximum concentration (C_max) and free area under the curve from time 0 to infinity (AUC_0–∞) for plasma were calculated as follows: fC_{max, plasma} = (1 – 0.893) × C_{max, plasma}, fAUC_{0–∞, plasma} = (1 – 0.893) × AUC_{0–∞, plasma}.

Results

The following values (mean ± standard deviation) were obtained: 0.06±0 L/h/kg for total clearance (CL_total), 0.44±0.06 hours for elimination-rate constant, 1.58±0.23 hours for half-life, 0.14±0.02 L/kg for steady-state volume distribution, and 2.28±0.33 hours for mean residence time. Time to C_max was 3.0 hours for plasma and skin tissue. C_max and AUC_0–∞ for plasma were 175.8±5.1 μg/mL and 811.8±31.9 μg × h/mL, respectively. C_max and AUC_0–∞ for skin tissue were 19.1±1.7 μg/mL and 113.9±21.8 μg × h/mL, respectively. Furthermore, fC_max and fAUC_0–∞ for plasma were 18.8 μg/mL and 86.9 μg × h/mL, respectively. The degrees of skin-tissue penetration, defined as the C_{max, skin tissue}/fC_{max, plasma} ratio and AUC_{0–∞, skin tissue}/fAUC_{0–∞, plasma} ratio, were 1.0 and 1.3, respectively.

Conclusion

Daptomycin exhibited good penetration into skin tissue, supporting its use for the treatment of complicated skin and skin-structure infections. However, further studies are needed in infected patients in order to investigate the relationship between the antimicrobial efficacy of daptomycin and its drug concentrations in skin tissues.

How do we use therapeutic drug monitoring to improve outcomes from severe infections in critically ill patients?

High mortality and morbidity rates associated with severe infections in the critically ill continue to be a significant issue for the healthcare system. In view of the diverse and unique pharmacokinetic profile of drugs in this patient population, there is increasing use of therapeutic drug monitoring (TDM) in attempt to optimize the exposure of antibiotics, improve clinical outcome and minimize the emergence of antibiotic resistance. Despite this, a beneficial clinical outcome for TDM of antibiotics has only been demonstrated for aminoglycosides in a general hospital patient population. Clinical outcome studies for other antibiotics remain elusive. Further, there is significant variability among institutions with respect to the practice of TDM including the selection of patients, sampling time for concentration monitoring, methodologies of antibiotic assay, selection of PK/PD targets as well as dose optimisation strategies. The aim of this paper is to review the available evidence relating to practices of antibiotic TDM, and describe how TDM can be applied to potentially improve outcomes from severe infections in the critically ill.

Population pharmacokinetics of daptomycin in patients affected by severe Gram-positive infections

A population pharmacokinetic analysis of daptomycin was performed based on therapeutic drug monitoring (TDM) data from 58 patients receiving doses of 4-12 mg/kg for the treatment of severe Gram-positive infections. At a daily dose of 8 mg/kg, daptomycin plasma concentrations (mean ± S.D.) were 76.9 ± 9.8 mg/L at the end of infusion and 52.7 ± 15.4 mg/L and 11.4 ± 5.4 mg/L at 0.5 h and 23 h after drug administration, respectively. The final model was a one-compartmental model with first-order elimination, with estimated clearance (CL) of 0.80 ± 0.14 L/h and a volume of distribution (V(d)) of 0.19 ± 0.05 L/kg. Creatinine clearance (CL(Cr)) was identified as having a significant influence on daptomycin CL, and a decrease in CL(Cr) of 30 mL/min from the median value (80 mL/min) was associated with a reduction of daptomycin CL from 0.80 L/h to 0.73 L/h. These results confirm that the presence of severe infection may be associated with an altered disposition of daptomycin, with an increased Vd. MICs were available in 41 patients and results showed that 38 and 31 subjects achieved AUC/MIC values associated with bacteriostatic (>400) and bactericidal effects (>800), respectively. Of note, 31 of these 41 subjects experienced a clinical improvement or were cured. Although daptomycin pharmacokinetics may be influenced by infections, effective AUC/MIC values were achieved in the majority of patients. The present model may be applied in clinical settings for a TDM routine on the basis of a sparse blood sampling protocol.

Comparative pharmacokinetic and pharmacodynamic evaluation of branded and generic formulations of meloxicam in healthy male volunteers

PURPOSE

The primary aim of the present study was to assess the pharmacokinetic bioequivalence between a generic formulation of meloxicam 15 mg tablets (Meloxicam Hexal) and its respective brand product (Mobic), in order to verify whether the generic product conforms to the regulatory standards of bioequivalence in the postmarketing setting. As a secondary exploratory aim, the pharmacodynamic effects of the two formulations were also evaluated by means of rating scales following hyperalgesia induced by cutaneous freeze injury.

SUBJECTS AND METHODS

A single 15 mg dose of generic or branded meloxicam tablets was administered to 24 healthy male volunteers in a crossover fashion. Plasma samples, collected for 24 hours after dosing, were assayed for meloxicam concentration by a validated highperformance liquid chromatography method.

RESULTS

THE ANALYSIS OF PHARMACOKINETIC PARAMETERS DID NOT SHOW ANY SIGNIFICANT DIFFERENCE BETWEEN THE TWO MELOXICAM FORMULATIONS: the 90% confidence intervals fell within the acceptance range of 80%-125% (0.84-1.16 for area under the curve [0-24], and 0.89-1.23 for peak concentration). No difference in the pharmacodynamic end point was observed between the two groups.

CONCLUSION

The pharmacokinetic profiles of the two meloxicam formulations confirm the regulatory criteria for bioequivalence; pharmacodynamic data indicate a similar antihyperalgesic effect. The two formulations can be used interchangeably in the clinical setting.

Cardiovascular implantable electronic device endocarditis treated with daptomycin with or without transvenous removal

BACKGROUND AND METHODS

Nine patients with cardiovascular implantable electronic device (CIED) endocarditis were treated with daptomycin after the failure of previous treatment. The blood and CIED lead cultures of 1 patient were negative. In the other 8 patients, we observed 6 monomicrobic infections and 2 polymicrobic infections. Overall, 10 strains were isolated in these patients: 4 methicillin-sensitive Staphylococcus aureus, 2 methicillin-sensitive Staphylococcus epidermidis, 1 methicillin-resistant Staphylococcus aureus, 1 methicillin-resistant Staphylococcus epidermidis, 1 methicillin-sensitive Staphylococcus hominis, and 1 Propionibacterium acnes. The CIED was removed transvenously in 7 patients. Two patients were too sick for the removal of their CIED, and were cured with 6 mg/kg of daptomycin for 60 and 110 days, respectively, without adverse events.

RESULTS

One patient died 4 days after the removal of his CIED because of a complicated abdominal aortic aneurysm. The other 8 patients were cured, with a mean follow-up of 17 ± 8 months. The removed leads were negative, after daptomycin therapy, in 4 cases out of 7. The mean ratio between peak daptomycin concentration and minimal inhibitory concentration (MIC) of the causative strains was 38.3 ± 18.5. For patients whose data were available, the ratio between peak daptomycin concentration and minimal bactericidal concentration (MBC) was 13.2 ± 3.2.

CONCLUSION

Daptomycin monotherapy may be a useful therapeutic tool in difficult-to-treat CIED endocarditis, resulting in a high rate of cures and sterilized leads removed. The ratio between peak daptomycin concentration and MIC or MBC may be useful as predictive tool for treatment success.

Daptomycin concentrations in valve tissue and vegetation in patients with bacterial endocarditis

In a patient with mitral-aortic native-valve Streptococcus oralis endocarditis, daptomycin concentrations in aortic and mitral valves were 8.6 and 30.8 μg/g, respectively, and 26 μg/g in the mitral vegetation. In the case of porcine-aortic-valve Staphylococcus epidermidis endocarditis, the daptomycin concentrations were 53.1 μg/g in the valve and 18.1 μg/g in perivalvular tissues. Daptomycin achieved apparently adequate tissue concentrations. S. epidermidis was eradicated, whereas Streptococcus oralis persisted, and its daptomycin MIC displayed a 4-fold increase.

Case report of a successful treatment of methicillin-resistant Staphylococcus aureus (MRSA) bacteremia and MRSA/vancomycin-resistant Enterococcus faecium cholecystitis by daptomycin

A 72-year-old man, receiving 8 mg daptomycin/kg body weight/day for methicillin-resistant Staphylococcus aureus (MRSA) bacteremia, was diagnosed with MRSA/vancomycin-resistant Enterococcus faecium (VRE) cholecystitis (daptomycin MIC values, 1 and 2 mg/liter, respectively). After the fifth drug dose, the bile concentration of daptomycin was 66 mg/liter 5 min after drug administration, with the biliary concentration/MIC values higher than 30 for both bacterial strains. Therefore, daptomycin achieved therapeutic levels in bile, hence suggesting a role for the drug in the treatment of MRSA/VRE cholecystitis.

Pharmacological issues of linezolid: an updated critical review

Linezolid is the first oxazolidinone agent introduced into clinical practice for use against Gram-positive bacteria that are resistant to beta-lactams and glycopeptides, including methicillin (meticillin)-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE). An optimal antibacterial effect is achieved when plasma drug concentrations are above the minimum inhibitory concentration (MIC) [T>MIC] for the entire length of treatment and the ratio between the area under the plasma concentration-time curve (AUC) and the MIC (AUC/MIC) is greater than 100, as is most commonly obtained with administration of the standard dosage of linezolid 600 mg twice daily. A wide tissue distribution, including the CNS and respiratory tract, nearly linear pharmacokinetics and good tolerability are additional characteristics of linezolid. However, variability in the drug pharmacokinetics associated with clinical conditions (e.g. sepsis, burn injuries, end-stage renal disease, cystic fibrosis), haemodialysis and/or young age may lower the T>MIC and the AUC/MIC ratio, thus impairing both antibacterial activity and prevention of mutants. In most cases, changes in the dosage or in the schedule of administration (e.g. an additional [third] daily dose) may improve the effectiveness of linezolid. It is worth noting that linezolid could affect its own metabolism as a result of protein synthesis inhibition in mitochondria, and this could lead to high plasma concentrations and an increased risk of non-negligible toxicities. The latter may be reported during long-term administration of linezolid or in the presence of some pathological conditions (e.g. renal disease or kidney transplantation) associated with high plasma drug concentrations. Therefore, treatment optimization should be considered a requirement for more effective and tolerable use of the drug, particularly in special populations.